CAUTION: The fuel system on K bikes is pressurized by the fuel pump. If your bike has been run recently then there will be pressure built up in the fuel lines. If you're going to be to disconnecting any fuel lines then it's advisable to wear some safety glasses and not to use a Bic lighter or a Tiki torch as a worklight. When you disconnect a pressurized line then chances are that some gas will be sprayed around. You might want to have some rags around to clean up any spilled gas.
0) If you can, run the tank fairly low before removing it. That will make it lighter and easier to work with. Also, you're better off putting the bike on the center stand before doing any of this.
1) Remove the seat and side(battery) covers.
2) Follow the clump of four wires coming from underneath the rear of the fuel tank and find it's connector under where the right battery cover was before you removed it. Disconnect that and get the clump of wires free so that you will be able to pull the tank back.
3a) 85 and earlier K100s: Remove the 10mm hex bolt that holds down the bracket on the rear of the tank.
3b) All other K bikes: There are two posts at the rear of the tank that go through some black rubber grommets in the frame. Under each grommet is a large (usually shiny) C-clip with a lip on it that fastens around each of two posts at the rear corners of the tank. Grab the lip of each C-clip from the side with some needlenose pliers and pull the C-clip straight back twoards the rear of the bike.
4) Lift the rear of the tank and pull the tank backwards. Sometimes, if it hasn't been removed in a while, the posts will stick in the grommets. I usually use a short section of 1x2 or 1x4 lumber to pry the rear of the tank up.
5a) 2 valve K bikes: There isn't a lot of slack in the fuel lines so you won't be able to pull the tank back very far without disconnecting the fuel lines. If you're just going to be working in the relay box then you can often get away with just propping up the rear of the tank with a block of wood. For anything more serious you're going to have to remove the fuel lines from the front left corner of the tank.
5b) 4 valve K bikes: There's a fair amount of slack in the fuel lines. Many times you can get away with just pulling the tank back or putting a tall chair next to the bike and supporting the tank that way without having to remove the fuel lines. (Put some towels/rags over the painted bodywork to avoid paint damage if you're going to use this approach.)
Side note: Under the right rear of the tank are two pipes pointing straight down. The front one was part of CA emissions crap and may or may not be connected to a pipe on the top front of the engine block. It doesn't matter. The rear one is for fuel overflow and comes from the hole on the left side under the gas cap. Some bikes have a hose connected to that that runs down the right side of the bike and drains to the ground inside of the right pegplate.
Other bikes have what commonly referred to as "the cup" mounted to the frame underneath those two pipes. The cup should be connected to a hose that runs down the right side of the bike and drains to the ground inside of the right pegplate.
The BMW part name for the cup (red item above) is "air accumulator" and it's part number is 16132307467. The drain hose (green item above) is part 16131455350.
Gas draining into the cup is why you might get a faint whiff of gas after filling up on a hot day.
6) Removing the fuel lines: (Remember that there may be pressure in the fuel system.) The fuel lines attach under the front left of the tank. Remove the rear one (that goes to the fuel rail) first. Remove the front one (that goes to the fuel pressure regulator) next. Note that if there's any appreciable amount of gas in the tank that the front one will leak gas so put your finger over it when lifting the tank off. (That's why you do that one last.)
7) Put a rag on the ground to keep from scratching the paint and place the tank against a wall with the front tilted upwards to keep gas from leaking from the front pipe.
8.) Installation is the reverse of removal. However, here's a few things to note:
- If you don't have the cup then make sure you attach the drain hose to the right rear pipe and that the hose is not kinked when the tank is installed. If you forget to attach that drain hose then you run the risk of draining gas onto a hot engine block which is generally considered dangerous and a fire hazard.
- Sometimes it's hard to get the tank far enough forward for the posts at the rear of the tank to align with their grommets. Straddle the bike, sit on it where the seat should be and push the tank forward with your hands at the lower rear corners, being careful not to push the bike off of the center stand.
- Applying some Armor All (or even some spit) to the grommets should help the posts slide down through their grommets more easily.
- To get the posts through the grommets far enough to re-attach the C-clips with needlenose pliers, stand on the side of the bike and lean over the bike with the weight of your stomach on the rear of the tank to push the posts down through the grommets.
- Finally,
don't forget to re-attach the fuel tank wiring connector.edit by scott_ 10-20-13 to replace missing photo
